Closing unit for a shaping machine

ABSTRACT

A closing unit for a shaping machine includes mutually moveable mold mounting plates suitable for carrying mold tool portions, a first hydraulic cylinder adapted to apply a closing force to the mold mounting plates, a second hydraulic cylinder, and a pressure storage means connected to the first hydraulic cylinder and adapted to store a pressure prevailing in the at least one first hydraulic cylinder upon pressure relief as a storage means pressure. A hydraulic interconnection of the pressure storage means with the second hydraulic cylinder allows the storage pressure stored in the pressure storage means to be used for locking and/or unlocking the locking device.

BACKGROUND OF THE INVENTION

The present invention concerns a closing unit for a shaping machine.

Shaping machines can be understood to be injection molding machines,injection presses, presses and the like. Hereinafter, the state of theart is outlined by reference to the example of injection moldingmachines. Similar problems and corresponding details however also applyin regard to other shaping machines.

Hydraulic closing units of the general kind set forth have at least onefirst hydraulic cylinder which serves to apply a closing force tomutually moveable mold mounting plates. As a result tool portions whichare to be mounted to the mold mounting plates are pressed against eachother. After the closing force has been built up a shaping process iscarried out. For example a plasticized plastic can be injected into themold which is subjected to the action of the closing force (injectionmolding process). Alternatively for example a reactive mixture can beintroduced into the mold and cured therein.

There are various kind of structure for common closing units, includingfor example two-plate closing units having four bars or a central pushrod. Three-plate machines with four bars are however also known.

As the at least one first hydraulic cylinder in many cases has togenerate a considerable force (power stroke) in many cases there is aseparate fast stroke in order to be able to move the mold mountingplates relative to each other at a higher speed. That makes it necessaryat the same time for the at least one first hydraulic cylinder and/orone of the mold mounting plates to be locked relative to at least onepull or push rod so that, after the fast stroke movement has beenperformed, the closing force can be built up. That at least one lockingdevice can be actuated by means of at least one second hydrauliccylinder which for example moves halves of a split nut relative to eachother. In a closed position an internal profile of the split nut thenengages into an external profile on the at least one pull or push rod.

The closing force can be reduced after the shaping process has beencarried out so that the closing unit can be opened and the molding cansubsequently be removed.

It is known from DE 10 2012 104 251 to load a hydraulic storage meansupon pressure relief to reduce the closing force. The energy stored inthat way is used in the next shaping cycle for again building up theclosing force. By virtue of the high pressures which have to be achievedwhen applying the closing force in the at least one first hydrauliccylinder and by virtue of the pressure loss which inevitably occurs uponstorage of the energy in the hydraulic storage means, the amount ofenergy which is actually re-used is however relatively slight incomparison with that which is used for applying the closing force.

DE 10 2007 011 442 A1 discloses a closing unit with a hydraulic powerstroke and electrically driven fast stroke. In that case it is proposedthat the energy which is recovered from an electrically driven faststroke movement is stored hydraulically and used for applying theclosing force or for further fast stroke movements. In that respectthere is naturally the disadvantage that the energy involved in applyingthe closing force is not re-used at all and further use of the energyfrom the fast stroke for applying the closing force is quiteinefficient.

SUMMARY OF THE INVENTION

The object of the present invention therefore is to provide a closingunit which allows more efficient re-use of the energy employed forapplying the hydraulic closing force than is the case in the state ofthe art.

That object is achieved by a hydraulic interconnection of the pressurestorage means with the at least one second hydraulic cylinder, by meansof which interconnection the storage pressure stored in the pressurestorage means can be used—for example for locking and/or unlocking theat least one locking device or for driving a hydraulic core pull means.

In closing units in the state of the art, the hydraulic systems forapplying the closing force and for further systems like, for example,the locking means are implemented separately from each other as, in theoperation of applying the closing force, pressures which are a multiplehigher occur than is the case in the other systems.

The invention is therefore based inter alia on the realization that itis possible to accept connecting the hydraulic systems for applying theclosing force and the other systems together. The pressure loss whichinevitably occurs upon storage of the hydraulic energy from applying theclosing force no longer occurs as a disadvantage in the case of theinvention because the other systems in any case operate with a lowerpressure.

Advantages of the invention are inter alia that firstly a large part ofthe energy which is liberated when reducing the closing force can berecovered and re-used. For example only relatively low pressures andsmall amounts of oil are usually necessary for the locking action andfor example an associated locking and unlocking movement is necessarilyperformed in the automatic cycle of an injection molding machine or inother shaping machines, at each production/reduction of closing force.Therefore with a suitable design of accumulator and locking cylindersecondly no additional supply for the locking action by way of a pumpwould be necessary and also the dynamics of the locking movement wouldbe improved by virtue of a supply by means of an accumulator, which canbe reflected in a saving in terms of cycle time.

In particular hydraulic oil can be used as the hydraulic fluid.

The at least one second hydraulic cylinder is a hydraulic cylinder whichis independent of the closing force actuation (the at least one firsthydraulic cylinder).

In addition, a shaping machine has a closing unit according to theinvention.

A pull or push rod can be provided for the transmission of the closingforce from the at least one first hydraulic cylinder to the moldmounting plates and at least one locking device for locking the at leastone pull or push rod relative to one of the mold mounting plates and/orrelative to the at least one first hydraulic cylinder.

The at least one locking device can preferably be actuated by the atleast one second hydraulic cylinder which moves, for example, halves ofa split nut relative to each other. In a closed position, an internalprofile of the split nut can then engage into an external profile on theat least one pull or push rod.

The at least one second hydraulic cylinder can also be adapted to drivea hydraulic core pull means.

Preferably, there is exclusively the storage pressure stored in thepressure storage means as the pressure source for the at least onesecond hydraulic cylinder for unlocking and/or locking. That measuremakes it possible to avoid a separate hydraulic system for the lockingaction, as far as possible. Self-evidently in that respect, it ispreferred if the at least one second hydraulic cylinder is the exclusivedrive for the at least one locking device. It is possible to providesomething similar for a core puller driven by the at least one secondhydraulic cylinder.

Particularly preferably, the storage means pressure can be between 10bars and 100 bars, preferably between 15 bars and 50 bars andparticularly preferably between 20 bars and 40 bars.

At least one pressure intensifier can be connected between the at leastone first hydraulic cylinder and the pressure storage means. The storagemeans pressure and/or a volume of the hydraulic fluid in the pressurestorage means can be so adapted in that way that the storage meanspressure and/or the volume is suitable for the design of the at leastone second hydraulic cylinder and/or the at least one locking device. Inother words, it is thereby particularly simply and reliably possible ineach shaping cycle to store so much hydraulic energy that it issufficient for unlocking and locking the at least one locking device.

It should be mentioned that the term pressure intensifier is used todenote both devices for producing a pressure intensification and alsodevices for producing a pressure reduction.

There can be provided a plurality of stages of different pressureintensification and/or pressure reduction, wherein preferably there canbe provided a pressure-reduced stage, a direct stage and apressure-intensified stage. The adaptation referred to in respect of thestored volume under the stored storage means pressure can thereby bematched even more precisely. The term a direct stage is used to denotethat there is neither a pressure intensification nor a pressurereduction.

The plurality of stages in respect of pressure intensification and/orpressure reduction can be implemented by a pressure intensifier, thehydraulic circuitry of which can be selected by means of a switchingvalve. In that way, it is possible to avoid manufacturing complication(and thereby costs), insofar as fewer pressure intensifiers or only onepressure intensifier have to be used.

Naturally the various stages can also be implemented by a plurality ofdifferent pressure intensifiers.

It is moreover also possible for both measures to be combined and forsome of the stages to be embodied by a single pressure intensifier andfurther stages embodied by a plurality of different pressureintensifiers.

The pressure storage means can be in the form of a bladder storagemeans. Bladder storage means can be produced by way of a bladder whichis filled for example with a compressible gas (for example molecularnitrogen), which is arranged in a pressure vessel. When filling thepressure vessel with hydraulic fluid under pressure the bladder iscompressed and the hydraulic energy is stored in the stressedcompressible gas.

It is possible to provide four pull rods which preferably pass throughthe mold mounting plates.

There can also be four first hydraulic cylinders which are respectivelyassociated with a pull rod and which are preferably arranged at a sideof a mold mounting plate which is fixed relative to a machine frame, theside facing away from a mold mounting plate which is moveable relativeto the machine frame.

There can also be a central push rod associated with a single firsthydraulic cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and details of the invention will be apparent fromthe Figures and the associated specific description. In the Figures:

FIG. 1 shows an embodiment of a hydraulic circuit according to theinvention of a closing unit,

FIG. 2 shows a further embodiment of a hydraulic circuit according tothe invention of a closing unit,

FIG. 3 shows graphs to illustrate the mode of operation of the hydrauliccircuit of FIG. 2,

FIG. 4 shows a further embodiment of a hydraulic circuit according tothe invention of a closing unit with pressure intensifiers,

FIG. 5 shows a further embodiment of the hydraulic circuit of a closingunit with a single pressure intensifier, and

FIG. 6 shows a side view of a shaping machine in the region of theclosing unit in which the invention can be used.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the state of the art at the present time, in ahydraulic injection molding machine or a press, the build-up of closingforce is achieved by the compression of hydraulic fluid (=pressureincrease) in suitably large hydraulic cylinders (the at least onehydraulic cylinder 3). In a structural configuration of injectionmolding machines from the applicant (DUO-Machines) that is implementedfor example by means of four large pressure cushion cylinders, whereinthe transmission of force is effected by way of four pull rods 4 (alsoreferred to as frame bars) and the at least one locking device 5. Inthis example there are provided four locking devices—one for each bar—atthat mounting plate 2 which is moveable in relation to a machine frameand the other mounting plate 2. The oil volume required for producingthe closing force is produced in that case from the short strokenecessary for overcoming the mechanical clearances, the compressionvolume of the hydraulic fluid, bar extension and plate flexing of themold mounting plates 2.

In the reduction in closing force usually the hydraulic fluid which isunder a high pressure is simply discharged to a tank in practice, inwhich case the stored energy of the compression volume of the fluid, themechanical extension of the bars and plate flexing is lost without beingused. Now the aim of the invention was to make it possible to better usethat energy again, that is to say to a higher proportion thereof, thanis proposed in the patent literature.

In the first embodiment shown in FIG. 1 for that purpose the hydrauliccircuit in the reduction in closing force is initially of such a formthat at any event in the first phase of pressure relief in the reductionof closing force (high-pressure phase) the fluid is not discharged to atank, but a pressure storage means 7 in the form of a hydraulicaccumulator (for example a bladder storage means) is loaded therewith upto a certain storage means pressure. The residual pressure of theclosing force system can then be discharged for example to a tank inorder to completely shut down the closing force. The pressure storagemeans which is charged in that way will be further used as a drivesource for movements involving a lower need for pressure and amount,more specifically the at least one locking device for example of apressure cushion machine.

The pressure storage means 7 is prestressed with a comparatively low gaspressure p₀ (for example p₀=40 bars). With a further pre-charge from abase pressure in the hydraulic system it is possible to provide asomewhat higher base pressure p₁ (for example p₁=50 bars) in thepressure storage means 7.

Here follows a brief operational sequence description of the build-up inclosing force and reduction in closing force, in accordance with theembodiment shown in FIG. 1.

The first step is the build-up of closing force by way of the pump 12and valve W1 in the pressure cushions (first hydraulic cylinder 3) bycompression of the oil to for example about 250 bars.

In the reduction in closing force now in the first phase the valve W3 isswitched and thus both the compressed oil and that volume of oil whichoccurs due to the relief stroke involved in bar extensions is fed fromthe pressure cushions (hydraulic cylinder 3) to the pressure storagemeans 7.

As the pressure storage means 7 is prestressed with a comparatively lowgas pressure it is now charged to a pressure equalization state asbetween the pressure cushion chambers and the pressure p_(Akku) in thepressure storage means 7.

Depending on the selected size of the pressure storage means 7 thepressure rise in the accumulator in the present embodiment is at about10 bars. In other words, the compression volume of the pressure cushionsby the reduction in pressure from 250 bars to 60 bars together with thestroke of bar stress relief and plate stress relief is now stored in thepressure storage means 7 at around 60 bars.

By way of the pressure sensors 13 (closing force) and 14 (p_(Akku)) itis recognized the extent to which pressure equalization has occurred.Upon approximation of the two pressures (˜60 bars) the valves W2 and W3are switched and the remaining closing pressure reduction can take placeto the tank 15.

The stored energy of the pressure storage means 7 is now available byswitching of the valve W4 at any time for other movements with a lowlevel of pressure consumption (for example locking or core pull).

FIG. 2 shows a further example with locking cylinders as consumers, therelevant volumes (V1-V3) and the pressures also being shown.

By reference to FIG. 2 it will now be shown how the volume ratios of theat least one first hydraulic cylinder 3 (pressure cushion cylinder) andthe at least one second hydraulic 6 (locking cylinder) can beimplemented in order to be able to use the function according to theinvention to the best possible degree. In that respect:

V₁ denotes oil volume on the rod side pressure cushion cylinder+linevolume

V₂ denotes the maximum piston volume locking cylinder

V₃ denotes maximum rod volume locking cylinder

V_(Δs) change in volume due to bar extension and plate flexing

_(Δ)s denotes bar extension+plate flexing under closing force

_(Δ)V₁ denotes compression volume in the pressure cushion under closingforce

_(Δ)p_(v1) denotes pressure difference between maximum closing pressureand maximum accumulator charging pressure (storage means pressure)

K denotes compression module.

The following applies for the compression volume _(Δ)V₁:

_(Δ) V ₁ =V _(1*Δ) p _(v1) /K

The total available volume V_(verf) due to the reduction in pressure inthe pressure cushions (first hydraulic cylinder 3) is composed of thecompression volume _(Δ)V₁ and the volume change V_(Δs) due to therestoration of the bar extension and plate flexing:

V _(verf)=_(Δ) V ₁ +V _(Δs)

In order to have stored sufficient hydraulic fluid for a cycleimplementation in the pressure storage means 7 (to lock at least onceand unlock once) V_(verf) must be somewhat greater than the overallpossible oil volume of the locking cylinders at the piston and rod side:

V _(verf>) V ₂ +V ₃

FIG. 3 finally shows an operational diagram involving the configurationsof closing pressure in the pressure cushion (p_(v1)), accumulatorpressure (p_(Akku)) and the associated switching positions of therelevant directional control valves W1 through W6 shown in FIG. 2 for acycle which includes the actions closing force reduction/accumulatorcharging, unlocking and locking again.

Firstly the pressure p_(v1) in the at least one first hydraulic cylinder3 under the closing force is at a maximum value p_(V1max). By opening ofthe valve W3, the pressure in the at least one first hydraulic cylinder3 is reduced to a value p_(V1min) and the pressure in the pressurestorage means 7 rises to a storage means pressure p₂. At that time, thevalve W2 is opened and the valve W3 is closed. As a result the storagemeans pressure p₂ in the pressure storage means 7 is stored and theresidual pressure in the at least one first hydraulic cylinder 3 isdischarged to the tank. By switching of the valves W5 for unlocking theat least one locking device 5 and W6 for the locking action that affordsthe possibility of opening the closing unit for example by a separatefast stroke, removing a produced molding and closing the closing unitagain, before the closing force can be built up again in a next cycle,after locking has taken place.

In the pressure configuration graphs shown in FIG. 3, it can also beseen that it is precisely at the beginning of the reduction in closingforce that there is a very high pressure excess available: about 250bars in the pressure cushion (first hydraulic cylinder 3) and theminimal pressure in the pressure storage means 7 of about 50 bars. It isonly at the close of the reduction in closing force that the pressuresapproximate (at about 60 bars) when the maximum charging of the pressurestorage means 7 is reached.

Admittedly, that simple procedure provides that a part of the storedenergy is recovered, but nonetheless there are high losses due to thegreat pressure difference at the beginning and by virtue of the factthat the last 60 bars cannot be used in this example.

A further improvement in that respect can be achieved with embodimentsas shown in FIGS. 4 and 5. The above-described losses can be markedlyreduced by the use of pressure intensifiers (shown in the form ofpiston-cylinder units 9).

By virtue of the effective area relationships the pressure intensifiersshown in FIGS. 4 and 5 generate pressure intensifications of 1:2 orpressure reductions of 2:1.

Here follows a brief operational sequence description of the reductionin closing force corresponding to the embodiment of FIG. 4.

A first stage S1, closing force reduction from 250 bars to 125 bars:valve W7 is activated and thus the charged pressure cushion (firsthydraulic cylinder) is connected to the rod side of the pressureintensifier 9. That provides a pressure reduction of 2:1, whereby 125bars are applied on the piston side of the pressure intensifier, that isto say the pressure storage means side. By virtue of the reduction inthe pressure loss, at the same time a doubling of the volume of thehydraulic fluid to be stored in the pressure storage means 7 isachieved! Thus in the range of 250 bars to 125 bars double the volume ischarged in the accumulator, than in the structures shown in FIG. 1 orFIG. 2.

Second stage S2, reduction in closing force from 125 bars to 60 bars:valve W3 is now activated and the accumulator is charged directly fromthe pressure cushion as in the embodiments of FIG. 1 or FIG. 2, untilthe pressure in the pressure cushion has fallen to 60 bars. Theaccumulator is selected to be of such a size that in the presentembodiment only a pressure rise from 50 bars to about 57 bars wasachieved up to that time.

Third stage S3, closing force reduction from 60 bars to 30 bars: valveW8 is now activated and thus a further “reversed” pressure intensifiercylinder 9 with a 1:2 pressure intensification is brought into play. Forexample therefore 60 bars in the pressure cushion is increased to 120bars, thereby permitting further charging of the accumulator to ˜60bars. That can be operated until only about 30 bars prevail in thepressure cushion (first hydraulic cylinder 3).

Fourth stage, closing force reduction of 30 bars: residual discharge ofthe pressure cushion to the tank is effected by way of the valve W2.

By virtue of that procedure the charge volume is doubled and thepressure losses reduced in the first stage S1 while in the third stageS3 the usable pressure of the pressure cushion (first hydraulic cylinder3) is increased from 190 bars (250 minus 60 bars) to 220 bars (250 minus30 bars). The number or design configuration of the pressureintensifiers, in particular pressure intensification and pressurereduction ratios, can be expanded and refined as desired.

FIG. 5 shows a further simplified variant in which it is possible to usea pressure intensifier 9 by virtue of a change-over switching valve 11in both directions (first stage S1 and third stage S3). This has theadvantage that it saves on a pressure intensifier 9 and in addition thepressure intensifier 9 after each cycle is automatically in the nextstarting position again.

FIG. 6 shows a side view of a shaping machine 10—in this case aninjection molding machine—in the region of the closing unit 1, in whichthe invention can be used. It is possible to see the mold mountingplates 2, the first hydraulic cylinders 3 for applying the closingforce, the pull or push rods 4 (in this case pull rods) as well as thelocking device 5 driven by the second hydraulic cylinders 6.

By virtue of the side view only two portions of the first hydrauliccylinders 3 and the pull rods 4 respectively can be seen in FIG. 6, inwhich respect there are actually four respective portions. The situationis similar with the two second hydraulic cylinders 6 of the lockingdevice 5, of which only one second hydraulic cylinder 6 is to be seen.

REFERENCE NUMERALS

-   1 closing unit-   2 mold mounting plates-   3 at least one first hydraulic cylinder-   4 at least one pull or push rod-   5 at least one locking device-   6 at least one second hydraulic cylinder-   7 pressure storage means-   8 interconnection-   9 pressure intensifier-   10 shaping machine-   11 switching valve-   12 pump-   13 pressure sensor closing force-   14 pressure sensor pressure storage means-   S1-S3 stages-   W1-W8 valves

1. A closing unit for a shaping machine comprising: mutually moveablemold mounting plates suitable for carrying mold tool portions, at leastone first hydraulic cylinder adapted to apply a closing force to themold mounting plates, at least one second hydraulic cylinder, a pressurestorage means which is connected to the at least one first hydrauliccylinder and which is adapted to store a pressure prevailing in the atleast one first hydraulic cylinder upon pressure relief as a storagemeans pressure, and a hydraulic interconnection of the pressure storagemeans with the at least one second hydraulic cylinder, by whichinterconnection the storage means pressure stored in the pressurestorage means can be used for locking and/or unlocking the at least onelocking device.
 2. The closing unit as set forth in claim 1, furthercomprising at least one pull or push rod for transmission of the closingforce from the at least one first hydraulic cylinder to the moldmounting plates and at least one locking device for locking the at leastone pull or push rod relative to one of the mold mounting plates and/orrelative to the at least one first hydraulic cylinder, wherein the atleast one second hydraulic cylinder is adapted to lock and/or unlock theat least one locking device.
 3. The closing unit as set forth in claim2, wherein exclusively the storage means pressure stored in the pressurestorage means is present as the pressure source for the at least onesecond hydraulic cylinder for unlocking and/or locking in cyclic mode.4. The closing unit as set forth in claim 2, further comprising fourpull rods which preferably pass through the mold mounting plates.
 5. Theclosing unit as set forth in claim 4, further comprising four firsthydraulic cylinders which are respectively associated with a pull rodand which are preferably arranged at a side of a mold mounting platewhich is fixed relative to a machine frame, said side facing away from amold mounting plate which is moveable relative to the machine frame. 6.The closing unit as set forth in claim 2, further comprising a centralpush rod associated with a single first hydraulic cylinder.
 7. Theclosing unit as set forth in claim 1, further comprising a hydraulicallydriven core pull means and the at least one second hydraulic cylinder isadapted to drive the core pull means.
 8. The closing unit as set forthin claim 1, wherein at least one pressure intensifier is connectedhydraulically between the at least one first hydraulic cylinder and thepressure storage means.
 9. The closing unit as set forth in claim 8,further comprising a plurality of stages of different pressureintensification and/or pressure reduction, wherein preferably there areprovided a pressure-reduced stage, a direct stage and apressure-intensified stage.
 10. The closing unit as set forth in claim9, wherein the plurality of stages of pressure intensification and/orpressure reduction are implemented by a pressure intensifier, thehydraulic circuitry of which can be selected by means of a switchingvalve.
 11. The closing unit as set forth in claim 9, wherein theplurality of stages are embodied by a plurality of different pressureintensifiers.
 12. The closing unit as set forth in claim 1, wherein thepressure storage means is in the form of a bladder storage means.
 13. Ashaping machine comprising a closing unit as set forth in claim 1.